MANUFACTURE OF A REVERSED LAY STRANDED ASSEMBLY

Abstract: A method of manufacturing a stranded assembly of flexible elements for example an electrical or optical cable in which the lay of the elements is repeatedly reversed along the length of the assembly, comprises: (i) feeding the elements (X) into one end of a guide, the guide having an upstream region in which one internal lateral dimension thereof constrains the strands to lie in side-by-side relationship and in which an orthogonal internal lateral dimension is greater than the total width of the elements, and a downstream region in which the elements are forced into a generally cylindrical geometry; and (ii) removing the elements from the other end of the guide in the form of a stranded assembly (Y). The elements are fed into the guide at a higher speed than they are removed from the guide so that they are forced into a serpentine configuration in the guide, and in the downstream region the serpentine configuration is converted into a generally helical one in which the lay of the elements is repeatedly reversed.

Description: MANUFACTURE OF A REVERSED LAY STRANDED ASSEMBLY This invention relates to the manufacture of a stranded assembly of separately formed flexible elongate elements in which the direction of lay of the elements along the length of the assembly is reversed at regular intervals. It is common practice in the manufacture of a stranded assembly of separately formed flexible elongate elements, such as a multi-core electric power or communication cable, a multi-core optical cable and a steel hawser, to "lay-up" or helically wind separately formed flexible elongate elements in a layer or in each of two or more layers each in a single direction of lay. Where the stranded assembly comprises two or more layers of such helically wound elongate elements, it is also common practice for the direction of lay of the elements of adjacent layers to be of opposite hand. With a view to improving manufacturing output, it is sometimes the practice to wind the separately formed flexible elongate elements of a layer helically in such a way that the elements are wound a plurality of times in one direction of lay and are then wound a like plurality of times in the reverse direction of lay, this cycle being repeated throughout manufacture of the stranded assembly. One form of cable has been proposed in British Patent Specification No: 2,241,374 in which the direction of lay of the cable is reversed relatively rapidly, e.g. as the elements have made in the region of one revolution around the assembly or less. Such a form of cable has the advantage for example that it can be formed in indefinite lengths since it is not necessary to spool the elements on to bobbins before laying up, which restricts the length of the elements, and prevents tandem operation of machines before or after the laying- up process. In the method described in the above British patent specification the elements are formed into a ribbon which is wavy in the same plane as the ribbon, and the ribbon is bent into a cylindrical geometry. The present invention is concerned with an improved method of manufacturing this form of assembly. According to the invention there is provided a method of manufacturing a stranded assembly of flexible elements in which the lay of the elements is repeatedly reversed along the length of the assembly, which comprises: (i) feeding the elements into one end of a guide, the guide having an upstream region in which one internal lateral dimension thereof constrains the strands to lie in side-by-side relationship, and in which an orthogonal internal lateral dimension is greater than the total width of the elements, and a downstream region in which the elements are forced into a generally cylindrical geometry; and (ii) removing the elements from the other end of the guide in the form of a stranded assembly; the elements being fed into the guide at a higher speed than they are removed from the guide so that they are forced into a serpentine configuration in the guide, and in the downstream region the serpentine configuration is converted into a generally helical one in which the lay of the elements is repeatedly reversed. Preferably the guide has an internal configuration that is generally part conical, in which the said one internal lateral dimension is a radial dimension and the othogonal dimension is a circumferential dimension, the radius of the guide reducing in the direction of travel of the elements. In this form of guide the circumferential dimension of the guide preferably extends over an arc of the cone, and the angle of arc increases as the radius decreases, for example so that, at the downstream region of the guide it is substantially annular. The width or circumferential dimension of the guide will depend on the number and size of the elements, but it is advantageously at least twice the total width of the sum of the elements. There is, in theory no upper limit to the width of the circumferential dimension of the guide. It is in practice normally not more than four times the width of the sum of the elements but it may be as great as, for example, ten times the width of the sum of the elements. During the initial setting up of the equipment the exit for the elements from the guide may be prevented so that the elements in their flat formation act as weak struts and mechanically fail as struts until supported by the sides of the guide. The flat ribbon of elements thereupon initially assumes a single half wave formation and as a further length of elements is fed into the tube the formation within the tube sequentially forms one oscillatory cycle and then a progressively greater number of cycles depending upon the length of guide, its width and the length of elements fed into the guide without being allowed to exit the guide. This initial setting up establishes the formation of the serpentine element ribbon generation. Any longitudinal elements, including hydraulic or pneumatic tube or pipe and those that are normally employed to form electric or optical cable may be used in the process, for example solid or stranded conductor electrical wires, optical fibres and cables, cable armouring and the like. The elements may be unitary in construction, but composite elements may be employed for example twisted pairs of wires etc. The production of waved element ribbon may proceed by feeding the straight elements longitudinally into the tube at a constant and steady velocity "x". The same quantity of elements are removed from the tube as enter it by removing the waved ribbon from the tube at steady and constant velocity "y", where y is the velocity along the centre line of the waved ribbon, y is of lesser magnitude than x and is preferably given approximately by the relationship:- x * • ** y(l + (1.57e/q) 2 ) where:- e = Departure of element from the centre line q * = length of one half cycle along the centre line (half lay length) The waved ribbon so produced can, with benefit, have a larger amplitude of oscillation and can have a shorter wavelength than is ultimately required in the final assemblage. In this way a waved ribbon is formed which is easier to fold by a series of rollers, cones or the like and is produced from a rectangular tube of greater width and a correspondingly reduced exit velocity. The individual elements in this case can be bent beyond their elastic limit so that after substantial closure the velocity is adjusted to x to stretch the assemblage to produce the final assembly with the required cycle length. Even if no prior priming of the guide takes place with y less than x an automatic build up of elements takes place within the guide until the assembled elements take the correct form at the downstream end of the guide when stability is achieved. An important feature according to the invention is to cause closure to begin to take place within the guide by fabricating the guide with curved parallel (coaxial) sides at the top and bottom so as to cause the waved ribbon to be bent into the shape of an arc of a circle when viewed in cross-section. By reducing the radius of curvature of the parallel sides from the entrance to the exit of the guide the waved ribbon is caused to begin the ultimate closure process. In this preferred aspect the complete closure process may be achieved by the formation of a guide having corresponding convex and concave opposite sides formed by a cone which is coaxially located within a trumpet. The edges of the guide can be formed by the fitting of an appropriately shaped sheet spacer, e.g. a triangular one, to blank off part of the entrance to the device and provide a tube initially of equal width from edge to edge and of reducing radius of curvature as the exit is approached. As the waved ribbon formed initially in this curved tube passes on its way to the exit formed by the trumpet it enters a circular cross-section of reducing diameter which brings about a complete closure of the assembly. At the exit the diameter of the trumpet approximates to the ultimate assemblage diameter such as to give a clearance for the assembled elements to pass through. The input velocity remains at a value of x and the exit velocity is given by y substantially as given by the formula given above. In the preferred method, the longitudinal elements which are fed into the guide side by side are caused to be waved at a wave length which is shorter than is required in the ultimate assembly and the amplitude of the wave produced within the invention is greater than is required in the final assembly. As the waved ribbon approaches the exit orifice the wavelength is increased and the amplitude reduced to give a completely closed assembly with each element having been bent beyond its elastic limit to give a more mechanically stable assembly. After exit from the guide the assembly may be held in its cylindrical configuration, for example by locating a longitudinal tape around the assembly or by extruding a jacket thereon which may also impart a greater degree of longitudinal tensile strength to the assembly. The assembly preferably includes a longitudinally extending element for preventing straightening out of the elements under their own natural resilience or under tension. Such an element may be a central, straight, element around which the elements are stranded, a further layer of elements that may be laid up by a different technique, or a tape or jacket applied on to the stranded assembly. The strands that are laid up by the guide may constitute the only strands in the assembly or one or more other layers may be present. Thus, it is possible to pass a central strand or bundle of strands through a bore in the guide so that the assembly of elements is forced into a generally cylindrical geometry about the central strand or bundle of strands to form a multi¬ layer assembly. Alternatively or in addition, one or more additional layers may be located on top of the assembly, preferably also by a method according to the invention. It is possible to employ a number of guides in tandem to form a multi layer assembly. It is also possible to form a larger assemblage by feeding the output from a number of guides to feed into a larger guide to be assembled. Alternatively, it may be desirable to employ a composite guide for forming a multi-layer assembly in which elements in a plurality of layers are laid up in the same place. Such a method has the advantage that the quantity of scrap produced in the process is reduced due to the reduction in length of the equipment. In order to prevent the stranded assembly ballooning in the manner of a bird cage as it leaves the guide it is advantageous to apply some means that restricts radical enlargement of the assembly. For example one or more tapes may be wound round the assembly, a braid may be formed on it, one or more relatively wide tapes may be applied to the assembly, a sheath may be extruded on to the assembly or a combination of these means may be provided. One advantage of the cables formed by the method according to the present invention is that they are inherently torque-balanced throughout their length as each short length of lay is counterbalanced by the adjacent length of lay in the opposite direction, so that any tension in the cable produces torques of equal magnitude and opposite direction. In so called "SZ" cables that are wound a number of times in one direction before the direction of lay is changed tension in the cable will cause alternating lengths of the cable to be subject to torques of alternating direction. Conventionally wound cable can be torque balanced by winding different layers with opposite lays, but this is only applicable to multi-layer cables. The surfaces of the guides in contact with the longitudinal elements preferably have, with advantage, a low friction. This can be achieved simply by the application of talc, silicone spray or the like to the elements at entry to the guide. The friction can also be reduced by coating the surfaces with polytetrafluoroethylene or similar low friction coatings. The guides can incorporate rollers, spheres or beads to reduce the friction whilst the longitudinal elements pass through the guide system. Friction can also be reduced by the passage of air or other gas through the surfaces of the guides if these are made porous, and in addition a flow of air or gas from the entrance to the exit of the guide will aid movement of the elements and reduce friction. The flow of air or gas can be pulsed to overcome any friction between the surface of the elements and the guide. The use of air or gas in these ways also allows for the removal of heat and its dissipation from the guide system. The minimising of friction allows the elements to be bent and formed more easily within the guide and there is less generation of heat. The minimising of friction also reduces the forces necessary to produce the required behaviour of elements and to cause them to pass through the guide. It is important to maintain a difference between the input and output velocities x and y of the strands, and the relationship between x and y can be directly monitored and controlled in a conventional closed loop system. If y is too great then the guide will be deprived of elements, while if y is insufficient there will be a build up of elements within the guide. It is therefore desirable to have devices to detect each of these conditions and to correct accordingly. Alternatively a constant force input can be applied to the elements entering the guide so that the input velocity x alters to maintain a constant quantity of elements within the guide. There are many conventional ways of controlling the x/y ratio, and one simple method of control of the ratio x/y can be provided as described below. The input velocity x is achieved by feeding the straight elements to pass between two wheels where the tyres of the two wheels mesh together. One wheel has a rigid or semi¬ rigid solid tyre and the other wheel has a soft or pneumatic tyre that is compressible so that as the solid tyred wheel is forced against the soft tyred wheel an area of contact is formed between the two wheels and the elements passing between them. If the force being applied by the solid tyred wheel is increased the area of contact between the wheels and the elements is increased. One or other or both wheels may be driven by a suitable motor or other similar device so that the longitudinal elements are forced to have a velocity x towards the entrance of the guide. An identical set of two wheels is arranged just after the exit of the assembled elements from the guide. Sprockets are attached and fixed coaxially to each of the soft tyred wheels and connected together by means of a linked chain so that both soft tyred wheels rotate at the same angular velocity and in the same direction. With equal softness of the soft tyred wheels and with equal force applied by each of the solid tyred wheels the effective diameter of both of the soft tyred wheels is identical. If the softness is varied or the force applied is different, then the effective diameter of the soft tyred wheel is changed and the velocity of the longitudinal elements passing between them will be different. In the case of the present invention the first set of wheels feeding straight elements into the guide produces a velocity x in the elements. With equal softness for both soft tyred wheels but with a greater force applied by the solid tyred wheel at the exit of the guide the effective diameter of this soft tyred wheel is less than that of its counterpart at the entrance to the guide. The velocity of the elements y at the exit to the guide is less than that at the entrance in proportion to their respective effective diameters. The angular velocity of the entry solid wheel is proportional to the velocity of the elements x and the angular velocity of the exit solid wheel is proportional to the output velocity y so that by comparing these wheel speeds and causing the value of the differential speed to control the force on the exit solid wheel, a constant control of the relationship x/y is achieved. This can be arranged, for example, by driving two identical direct current generators one from each of the two solid tyred wheels at entry and exit positions. The output from the faster running entry generator supplies a voltage divider which is set to produce a voltage which is electrically set in opposition to the output from the slower running exit generator. Any differential voltage is supplied to an electric motor either directly or via a dc amplifier to drive a mechanism to alter the force applied by the exit solid tyred wheel. The applied force will be increased if the velocity y is too great and the force reduced if y is too small. When the correct relationship exists between x and y to maintain a constant length in the guide then the opposing voltages from input and output exactly match and zero voltage difference exists and there is no change in the force applied by the solid tyred exit wheel. All solid and soft tyres can have grooves incorporated with advantage to control and apply a force to any specific shape or numbers of elements or assemblages. Embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 shows in plan, end views and cross- sections the guide system; Figure 2 shows in perspective the guide system with an approximation of the location of the individual elements and their assemblage at a particular instant; Figure 3 illustrates the input and output drive mechanisms to give a constant relationship between the input and output velocities with a diagrammatic indication of an electrical/ mechanical control system to maintain a predetermined relationship between the input and output velocities; Figure 4 shows in perspective the total equipment for the manufacture of bi-directionally twisted elements with the control system not shown for clarity; and Figure 5 shows an alternative form of guide used for forming multi-layer assemblies. Referring to the accompanying drawings a rigid cone C is fitted within a trumpet T to form a guide such that a parallel sided space is provided between them in order that longitudinal elements X (shown in figure 2) have a clearance for movement but insufficient space for the elements to ride over one another ensuring that they maintain a substantially flat formation with respect to one another. A spacer S is fitted between the cone and trumpet of tapering width as shown in Figure 1 sections AA, BB, and DD to form the edges of the guide. This reduction of width of the spacer provides an annular space for the elements to be contained which has the same circumferential width although the radius of curvature of the annulus reduces as the elements pass into the guide from the entrance towards the exit orifice. The initial setting of the longitudinal elements within the guide establishes a waved ribbon with a magnitude determined by the width of the annulus. The waved ribbon of elements follows the reduction of annulus diameter as the elements move closer to the exit of the guide. Further towards the exit of the guide as shown in Section EE of Figure 1 where the spacer is no longer present and as the total annulus circumference between cone and trumpet reduces towards t the exit the waved elements are able to occupy the whole of the circumference and complete the closure as shown in Section FF to form the assembly Y. In order to establish and maintain a constant relationship between the input and output velocities of the elements it is necessary to have an input drive mechanism for the straight parallel elements that enter the guide side by side in a flat formation and the output drive mechanism which removes the assembled elements which have a circumscribing circular shaped cross-section moving at a velocity which is less than the input velocity as determined by the degree of bi¬ directional twisting and the number of twists per unit of length along the centre line of the assemblage. This relationship between the input and output velocities is necessary in order to maintain the same length of elements within the guide which in turn ensures the continuance of the pre-forming of the wave shape and the closure of the elements as indicated in Figure 2. Figure 3 shows the input drive mechanism comprising a solid tyred wheel G which is driven and interacts with a soft or pneumatic tyred wheel H to which a sprocket K is coaxially attached. The wheel G is forced towards the wheel H to cause a depression of the soft tyre of wheel G to give a length of contact with the elements X and impart a velocity x to these elements at entry. Either or both the tyres of G and H can be grooved to accommodate the ribbon elements X and establish their location. The output drive mechanism is composed of two identical wheels to the input mechanism with a wheel I having a solid tyre and wheel J a soft or pneumatic tyre. A linked chain M joins the two sprockets one on each of the two wheels H and J to ensure that wheel J is driven at the same angular velocity as wheel H. Wheel I is forced towards the wheel J to cause a greater depression of the soft tyre of wheel J than that experienced by the tyre of wheel H so that the effective diameter of wheel J is less than the effective diameter of wheel H at the point of contact with the elements. This reduction in diameter gives rise to a reduction of output velocity y of the assembled elements Y compared with the input velocity of the elements x of the unwaved elements X. Either or both the tyres of the wheels I and J can be grooved to accommodate the assembled elements Y and to establish their location. In this example two direct current electrical generators N and 0 of identical design are coaxially attached one to each of the same shafts as the wheels G and I respectively to give a voltage output proportional to the angular velocities or wheels G and I which are proportional to the velocities of the elements x and y. The output voltage from generator N is supplied to a voltage divider P to give a voltage which is exactly equal and opposite to the voltage produced by the generator 0 when the correct relationship exists between the velocities x and y. Any difference between the outputs from the potential divider P and the generator 0 is supplied to a dc electric motor Q, if necessary via a dc amplifier, to drive a gear wheel R which causes a gear U to rotate and force the wheel I to be raised or lowered by means of the screw thread V which passes through a tapped hole within a fixed plate W. If the velocity y is to great there is a potential difference between the outputs of P and 0 which supplied the motor Q and the wheel is driven down to reduce the effective diameter of wheel J until the velocity y is reduced to the required value when P and 0 produce equal and opposite voltages and stability is established. If velocity y is too small then the difference between the voltages produced by P and 0 are of the opposite sense and the motor Q is driven in the opposite direction to increase the effective diameter of wheel J and increase the velocity y to the required value. The example shown in Figure 3 is only one illustration of a control system which can be achieved by other conventional systems which may employ electrical alternating current or pulsed current steps. Different types of electric generators or motors can be used or the whole control system can be operated by hydraulic or by pneumatic conventional control systems. Control can also be achieved by directly establishing the situation within the guide by means of sensors to ensure the same quantity of elements remain within the guide. Figure 4 illustrates a typical complete assemblage plant with the control system for the velocities x and y not shown for clarity. Also the need for the control system may be found not to be necessary in some cases. The individual elements enter the plant via a flat tube ø which feeds the elements X in flat touching formation into the input drive mechanism formed by wheels G and H which force the elements forward at a velocity x towards the guide C T. In this case an eccentric thick disc rotates, guides and holds the elements in a deep groove in its circumference to maintain formation as they pass. This eccentric induces a predetermined wave shape to the ribbon of elements as it enters the annular space between the cone C and the trumpet T. The height of the space between the cone C and the trumpet T is established by the relative sizes of the guide and also the thickness of the spacer S which forms the sides of the part-circumferential annulus at entry and further towards the exit of the trumpet but is terminated before the exit of the trumpet as previously described. Within the guide the elements initially wave and assume a reducing diameter terminating at the exit to the trumpet as a totally closed assemblage. In this example a longitudinal tape Z is fed through a large ring 7j and thence a smaller ring 0- to cause closure of the tape around the assemblage Y. The longitudinal tape can be of the adhesive type on the side next to the assemblage and can be controlled by rollers in place of the rings and A. The longitudinal tape can be dispensed with or applied as required if the assembly is directly supplied to the input of an extruder to apply an overall sheath to act as a longitudinal tensile unit. The output drive consists of two wheels I and J with solid and soft/pneumatic tyres respectively. Wheel J is driven at the same angular velocity as wheel H by means of the sprockets K and L on wheels H and J respectively to which is attached a loop link chain M. The wheels G and I are forced on to the respective wheels H and J to cause depressions in the soft tyres to give greater grip with the elements X and Y respectively. The force on wheel I is such as to reduce the effective diameter of wheel J to less than that of wheel H so that the input velocity x is greater than the output velocity y by the required amount to ensure the same length and formation of elements is retained within the guide. A control system can be incorporated if found necessary as previously described or by any well established other method so that the relationship between input and output velocities x and y is maintained. A central longitudinal tensile element can be incorporated by feeding an element through the cone to emerge at the tip of the cone which continues within the trumpet and to be surrounded by the closing waved elements to form an assemblage with a central longitudinal tensile element. A similar system can be used to form multi-layer assemblies by feeding the output of the equipment described above to form a central element of another similar plant to allow further additional elements to be applied in a bi¬ directional way. Many sets of equipment can operate in tandem to make multi-layer assemblies of any required number of elements. It is possible to modify the arrangement shown in Figure 4 by incorporating an extruder between the output end of the cone and trumpet and the output drive wheels I and J, to extrude a jacket directly on to the stranded assembly thereby dispensing with the need for the tape 7. Alternatively the tape could be guided so that it wraps around the entire circumference of the assembly with a longitudinally extending overlap which can be sealed by electrical or heat welding in known manner. An alternative method of multi-element assembly can be achieved by feeding the output of several of the primary equipments into a larger similar equipment with each primary assembly acting in the same way as a single element to be assembled in a bi-directional fashion into a larger multi-element assembly. This method of manufacture can continue by tandem operations to form assemblies of any number of elements. The cone and trumpet combination can be formed in many alternative ways to provide a low friction guide for the elements through the space between cone and trumpet. Solid materials can be used with the surface friction reduced by a suitable coating such as polytetrafluoroethylene (PTFE) or similar materials, by the addition of talc or silicone spray on to the elements at entry or by the flow of gas or air through porous surfaces to keep the elements away from the actual solid surfaces this gas flow can be pulsed to overcome any friction, gas or air can also be caused to flow from the entrance towards the exit of the guide to assist the element movement. The use of gas also removes heat from the guide which is produced by friction. The guide can also be formed from a series of rollers, balls or beads held in place by frames which overall will reduce the friction experienced by the elements, allow forced or natural cooling to take place and to facilitate adjustment of cone and trumpet settings for different sizes of elements or numbers of elements to be assembled. Figure 5 shows a composite guide that may be employed for forming a multi-layer assembly. The composite guide is formed from a number of generally frusto-conical guide elements 51, 52 and 53 that are nested together. The innermost guide element 51 may have a solid centre or it may have a central core 54 through which a central element may be passed around which the other elements are laid, and the other guides 52 and 53 have hollow centres which can fit around guide 51 and any other guide located within it. The composite guide may be formed as a single assembly or the separate guides 51, 52 and 53 may be separate from one another. In the latter case the composite guide could be adjusted to accommodate the diameter of the elements by adjusting the axial positions of the guides relative to one another. In this case it may be necessary to employ spacers S of different thickness depending on the relative positions of the guides.

Claims: CLAIMS 1. A method of manufacturing a stranded assembly of flexible elements in which the lay of the elements is repeatedly reversed along the length of the assembly, which comprises: (i) feeding the elements into one end of a guide, the guide having an upstream region in which one internal lateral dimension thereof constrains the strands to lie in side-by-side relationship and in which an orthogonal internal lateral dimension is greater than the total width of the elements, and a downstream region in which the elements are forced into a generally cylindrical geometry; and (ii) removing the elements from the other end of the guide in the form of a stranded assembly; the elements being fed into the guide at a higher speed than they are removed from the guide so that they are forced into a serpentine configuration in the guide, and in the downstream region the serpentine configuration is converted into a generally helical one in which the lay of the elements is repeatedly reversed. 2. A method as claimed in claim 1, wherein the guide has an internal configuration that is generally part conical, in which the said one internal lateral dimension is a radial dimension and the orthogonal internal lateral dimension is a circumferential dimension, the radius of the guide reducing in the direction of travel of the elements. 3. A method as claimed in claim 2, wherein the circumferential dimension extends over an arc of the cone, the angle of arc increasing as the radius decreases. 4. A method as claimed in any one of claims 1 to 3, wherein in the downstream region the guide is substantially annular. 5. A method as claimed in any one of claims 1 to 4, wherein the elements are oscillated laterally as they are fed into the guide in order to assist them into a serpentine configuration in the guide. 6. A method as claimed in any one of claims 1 to 5, which includes passing a central strand or bundle of strands through a bore in the guide so that the assembly of elements is forced into a generally cylindrical geometry about the central strand or bundle of strands to form a multi-layer assembly. 7. A method as claimed in claim 6, wherein a central bundle of strands, which is itself a stranded assembly in which the lay of the elements is repeatedly reversed, is passed through the bore of the guide. 8. A method as claimed in any one of claims 1 to 7, wherein the assembly is held in its cylindrical configuration after it is removed from the guide. 9. A method as claimed in claim 8, wherein it is held in its cylindrical configuration by extrusion of a jacket thereon.

Inventors: GOSLING CYRIL HENRY, GOSLING, CYRIL, HENRY
Applicants: BICC PLC, GOSLING CYRIL HENRY, BICC PUBLIC LIMITED COMPANY, GOSLING, CYRIL, HENRY
Application year: 1994
Main classification: D07B3
IPC codes: D07B3, G02B6, H01B13